What is the management approach for a patient with hyponatremia?

Management of Hyponatremia

Initial Assessment and Classification

Begin by confirming true hypotonic hyponatremia through serum osmolality (<275 mOsm/kg) and exclude pseudohyponatremia from hyperglycemia by correcting sodium (add 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL). 1

• Assess extracellular fluid volume status through physical examination, looking specifically for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or peripheral edema, ascites, and jugular venous distention (hypervolemia) 2, 1
• Obtain serum and urine osmolality, urine sodium concentration, and urine electrolytes to determine the underlying cause 2
• Check serum creatinine, thyroid function (TSH), and cortisol to exclude endocrine causes 1
• Measure serum uric acid, as levels <4 mg/dL have a 73-100% positive predictive value for SIADH 2

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

For patients with severe symptoms, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, but never exceed 8 mmol/L total correction in 24 hours. 2, 1

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 3
• Monitor serum sodium every 2 hours during initial correction 2, 1
• Consider ICU admission for close monitoring during treatment 2

Mild to Moderate Symptomatic Hyponatremia

• For patients with nausea, vomiting, headache, or mild confusion, treatment depends on volume status and underlying cause 2, 4
• Monitor serum sodium every 4 hours after resolution of severe symptoms 2

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 2, 1

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on clinical response 2
• Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 2
• Continue isotonic fluids until euvolemia is achieved 2

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 2, 1

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 2
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 2, 5
• Alternative pharmacological options include urea, demeclocycline, or lithium 2, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and treat the underlying condition. 2, 1

• Discontinue diuretics temporarily if sodium <125 mmol/L 2, 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 2
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 2

Critical Correction Rate Guidelines

The maximum correction rate must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 2, 1, 3

• For average-risk patients: aim for 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 2
• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 2, 1
• For acute hyponatremia (<48 hours onset), more rapid correction is safer than for chronic hyponatremia 2, 6

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 2

• Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 2
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 2

Special Populations

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments. 2

• SIADH: euvolemic state, treat with fluid restriction 2
• CSW: hypovolemic state with CVP <6 cm H₂O, treat with volume and sodium replacement (isotonic or hypertonic saline), never fluid restriction 2
• For severe CSW symptoms, add fludrocortisone 0.1-0.2 mg daily 2
• In subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction 2

Cirrhotic Patients

Patients with cirrhosis and sodium ≤130 mEq/L have increased risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36). 2, 1

• Use conservative correction rates (4-6 mmol/L per day) due to higher risk of osmotic demyelination 2
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 2

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours - this causes osmotic demyelination syndrome 2, 3
• Inadequate monitoring during active correction increases risk of complications 2
• Using fluid restriction in cerebral salt wasting worsens outcomes 2
• Failing to recognize and treat the underlying cause leads to poor outcomes 2
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 2
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant, as it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 2, 3